高温高压深井地层测试工具低频度失效案例解析

Case Analysis of DST Tools Low-Frequency Failures in HTHP Deep Well

高温高压深井苛刻的井底工况,很容易使测试工具的缺陷和瑕疵扩大,从而造成地层测试作业的失败。测试作业人员如果没有丰富的经验以及充分的防范措施,很难确保测试作业的高成功率,尤其是一些低频度的工具失效形式,更是增加了测试失败的几率。文章针对在一些案例井中出现的RDS阀循环孔提前开启、RDS/RD阀循环孔无法开启、测试管柱发生单向串漏、油套压力间歇性窜漏等罕见的失效形式,经过逐步的解析,发现了破裂盘的焊接质量问题、密封圈抗气爆性能失效、套管的大尺度变形及磨损、温度效应造成管柱长度的大范围伸缩等潜在原因。从而提出了加大破裂盘的抽检比例,并且在其安装在外筒后,坚持按照破裂值80%试压;选择抗气爆性能优越的密封件;测试前开展套管磨损检测及分析计算;开展作业全过程管柱三轴应力分析计算等对应解决方案,进一步提高了入井工具应用的成功率。

The harsh downhole conditions in deep HTHP Well can easily lead to amplified defects and flaws of drillstem test(DST)tools,resulting in failure of DST operation.Without rich experience and adequate preventive measures,it is difficult to ensure a high success rate of test operation,especially some low-frequency tool failures,which may increase the chance of test failure.In some cases occurred unusual failures such as circulation hole of RDS valve opening in advance or circulation hole of RDS/RD unable to open,unidirectional leakage of testing tool,intermittent leakage between casing and tubing.Through gradual analysis,the potential causes were found such as welding quality problem of the rupture disk,failure of the resistance to air explosion of sealing ring,large-scale deformation of the casing and large-scale expansion of the string length caused by the effect of wear and temperature.Researches show that the success rate of tool application can be improved by increasing the proportion of random inspection of rupture disc and installing it outside of the outer barrel;selecting seals with superior gas explosion resistance;performing the casing wear detection and analyzing before testing;caring out the triaxial stress analysis and calculation of the whole operation process.